1. Field of the Invention
The present invention relates to an electronic endoscope apparatus having a video-scope with an image sensor. Especially, it relates to adjusting a brightness of an object image.
2. Description of the Related Art
In the electronic endoscope apparatus, an automatic brightness adjustment process is performed to maintain a proper brightness of an object image, which is displayed on a monitor. For example, an average luminance level of the object image, and a luminance-difference between the average luminance level and a reference luminance level indicating a proper brightness are calculated. Then, a diaphragm is opened or closed on the basis of the luminance-difference.
When using forceps, or supplying water for washing a lens and an observed portion, a minute luminance-change occurs. Also, while observing, the luminance level minutely changes due to the pulsatory motion. Since the brightness adjustment process responds to the fine luminance-change, the brightness on the monitor continuously changes in accordance with the motion of the diaphragm, which results in difficulty of viewing the observed portion.